1. Field of the Invention
The present invention relates to an unauthorized access prevention method, an unauthorized access prevention apparatus and an unauthorized access prevention program for preventing unauthorized access conducted from a network to a terminal.
2. Description of the Related Art
In recent years, IP (Internet Protocol) telephone and video phone have been put into practical use by using RTP (Real-time Transport Protocol) packets having codec signals in their payloads on the Internet.
In order to start a session of RTP packet transmission, signaling is conducted by using, for example, the SIP (Session Initiation Protocol) or H.323. A SIP message contains a SIP header and a SIP body, and the SIP body contains a description according to the SDP (Session Description Protocol).
While the session of RTP packet transmission is being executed, session control is conducted by using the RTCP (RTP Control Protocol).
As preceding technical papers relating to the present invention, the following papers can be mentioned:
RFC 3261 standards    http://www.ietf.org/rfc/rfc3261.txt
RFC 2327 standards    http://www.ietf.org/rfc/rfc2327.txt?number=2327
RFC 3550 standards    http://rfc3550.x42.com/
The first paper relates to the SIP. The second paper relates to the SDP. The third paper relates to the RTCP.
At the time of signaling and session execution, a virus is sent into a terminal sometimes as hereafter described.
A virus is made to conceal itself in a header or a payload of a signaling packet.
A large number of signaling packets are sent to cause overflow of a buffer and thereby prevent a virus check function from being effective.
At the time of signaling before starting the session, not only a port used to transmit video data or music data but also another port is opened to traffic. A virus is also transmitted by using the other port together with the video data or music data for streaming.